Caries, which is the most widespread infectious disease in humans, develops in the form of carious lesions when plaque bacteria, primarily mutans streptococci and lactobacilli, form organic acids by an anaerobic metabolism mechanism on fermentable carbohydrates. The acids diffuse into the hard tooth tissue and destroy the crystalline phases of the enamel and dentine. By the dissolving out of these minerals, irreversible structural changes are caused in the hard tooth tissue. This demineralization takes place from a pH of less than 5.5. A continuous precipitation of certain ions, such as calcium and phosphate ions, out of the saliva moreover occurs. The presence of these ions in the oral cavity leads to a remineralization. If fluoride is present, the remineralization is additionally promoted by the formation of acid-resistant fluorohydroxyapatite. In the dynamic medium of the oral cavity, demineralization and remineralization alternate. If an equilibrium exists between these processes, no caries develops. However, if the equilibrium is disturbed, the formation of a carious lesion is promoted by the increasing loss of inorganic constituents of the enamel.
Early detection of caries plays a decisive role in the fight against this disease, since the current state of knowledge is that a progression of caries can be arrested in any stage. If a lesion is detected in the early stage, the probability of successful remineralization is increased significantly. A (minimally) invasive treatment can thus be avoided under certain circumstances.
As a rule, the diagnosis of a carious lesion is made with the aid of a visual/tactile inspection of the particular tooth situation. If it is a matter of occlusal caries, as in most cases, correct diagnosis is an enormous clinical challenge to the dentist, since it is extremely difficult reliably to detect a lesion in fissures and pits even with the aid of a magnifying glass/probe. The difficulty of occlusal caries diagnostics results from the specific morphology of fissures and pits. For this reason alternative diagnostic methods have already been widely developed in the market.
There may be mentioned by way of example at this point methods for detection and for controlled monitoring of changes in the mineralized tissue by optical methods. U.S. Pat. No. 7,796,243 B2 thus proposes the use of optical coherence tomography in combination with Raman spectroscopy. US 2010/0227296 A1 describes methods for evaluation of risk factors with respect to oral health which are based inter alia on physical phenomena, such as luminescence, fluorescence and thermal emissions. US 2007/0021670 A1 relates to apparatuses for detection of caries, demineralization and remineralization which are based on IR photothermal radiometry and luminescence.
Contactless methods and devices which utilize the property of healthy and carious hard tooth tissue to fluoresce naturally have proved to be particularly suitable for detection of caries in particular, but also of plaque, concrements, bacterial attack on teeth etc. By irradiation with high-energy laser light of a particular wavelength, for example, carious regions can be excited to a more intense fluorescence than healthy hard tooth tissue.
DE 30 31 249 C2 describes an investigative method for detection of caries, wherein the tooth is irradiated with virtually monochromatic light. The light beam excites a fluorescence radiation on the tooth. The fluorescence spectrum then emitted by the tooth shows clear differences between carious and healthy regions of the tooth. Thus, in the red spectral region of the fluorescence spectrum of the tooth, between 550 and 650 nm, the intensity is significantly higher than in the case of a healthy tooth, based on incident light of a wavelength of 410 nm. In contrast, in the blue spectral region of the fluorescence spectrum of the tooth, between 350 and 450 nm, the intensity of the fluorescence radiation is almost identical for carious regions and healthy regions of the tooth. It has therefore been proposed to irradiate the tooth with a wavelength of 410 nm and, by means of two filters, to record the fluorescence radiation of the tooth for a first wavelength of 450 nm and a second wavelength of 610 nm, that is to say in the blue and red spectral region, for example with the aid of photodetectors. The fluorescence radiation intensities recorded by this arrangement are subtracted, so that on the basis of the difference in intensity thereby obtained, a healthy region of the tooth can be clearly distinguished from a carious region of the tooth.
An excitation wavelength of 488 nm is stated elsewhere (S. Albin et al., “Laser Induced Fluorescence of Dental Caries”, Proc SPIE 907, 96-98, 1988).
DE 42 00 741 C2 reports that a device for detection of caries is equipped with an excitation radiation having a wavelength in the range of from 360 nm to 580 nm and the fluorescence radiation caused on the irradiated tooth in the wavelength range between 620 nm and 720 nm is filtered out. By this measure the separation between the wavelength of the excitation radiation and of the fluorescence radiation emitted is said to be sufficiently wide so that the excitation radiation cannot falsify the results of the evaluation by overlapping the fluorescence radiation.
E. de Josselin de Jong et al. “A new Method for in vivo Quantification of Changes in Initial Enamel Caries with Laser Fluorescence”, Caries Research, 2-7, 1995 describes irradiation of the tooth with laser light of a wavelength of 488 nm, recording of the fluorescence radiation of the tooth for wavelengths from 520 nm via a CCD camera and mathematical evaluation of the data, in order to be able to detect a carious tooth region in this way.
DE 93 17 984 U1 discloses a device for detection of caries, wherein the excitation radiation is generated not continuously but in pulsed form during an excitation interval.
U.S. Pat. No. 7,596,253 discloses methods and devices for detection of caries, wherein fluorescence image data are generated and processed.
DE 297 04 185 U1 proposes a device for detection of caries, with which a tooth to be investigated is irradiated homogeneously and the excited fluorescence spectrum of the tooth is said to be recorded more accurately. The emission and recording equipment of this device has a plurality of individual emission fibres and detection fibres which can be arranged in alternation relative to one another. In particular, an emission fibre is said to be surrounded coaxially by several detection fibres.
DE 195 41 686 B4 describes a device for detection of caries, plaque or bacterial attack on teeth which is said to have improved properties. The wavelength of the excitation radiation generated by a light source here is between 600 nm and 670 nm.
DE 198 25 021 A1 describes methods and devices for detection of caries, plaque or bacterial attack on teeth, wherein the fluorescence radiation is evaluated with wavelengths above approx. 800 nm. A particularly sensitive recording of hidden caries, such as in fissures or in the approximal tooth region, is said to be achievable with this measure, since in this wavelength region the proportion of caries-specific fluorophores and other deposits is particularly high, but healthy tooth enamel or dentine gives out no or only little fluorescence.
Further methods and/or devices for detection of bacterial attack on teeth which are based on optical principles are to be found in the publications DE 197 09 500 C1, DE 202 09 441 U1, DE 102 27 128 A1, DE 603 16 699 T2, DE 196 19 067, DE 10 2005 052 294 A1, DE 94 17 470 U1 and DE 101 33 451 A1.
The now technically widely developed methods of diagnosis for early detection of caries must of course be accompanied by suitable therapeutic methods which have the effect that the caries attack does not progress further and stops, as far as possible avoiding an invasive intervention by the dentist. In this respect, sealing of teeth (in particular sealing of fissures and pits, but also in the sense of complete sealing of the tooth) with mechanically highly resistant, retention-secure, abrasion-resistant and readily flowable plastics compositions has proved to be appropriate.
“Sealing of fissures and pits” (also summarized as “sealing of fissures” in the following) is understood as meaning filling of the sometimes very deep pits, rough furrows and grooves on the surface of teeth with a readily flowing plastics material. The often narrow indentations on the chewing surfaces of a tooth are called fissures. In children and adolescents, but also in adults, caries often develops first in the fissures of the chewing surfaces, the occlusal surfaces of the lateral teeth displaying the highest susceptibility to caries. A highly developed and fissured relief is also to be found, for example, on the inside of the front teeth, so that here also sealing for prophylaxis of caries may be appropriate. In addition, a clearly pronounced fissure relief also promotes adhesion of plaque. Accumulation of plaque has also been observed in narrow fissures and on steeply sloped protuberances.
The various types of fissure (for example ampoule-shaped, I-shaped, U-shaped, V-shaped) can accommodate residues of food and therefore also offer an ideal and protected habitat for caries-causing bacteria, since oral hygiene measures, such as brushing teeth, do not reach here. The bristles of toothbrushes are in general too wide to be able to clean the base of the fissure. The morphology of the fissures therefore makes mechanical cleaning of the pits almost impossible. If an enamel caries were to arise in the fissure, it will highly probably spread very rapidly into the dentine, since the thickness of the enamel in the region of the fissure, especially at the base of the fissure, as a rule is very thin. The high susceptibility of fissures to carious attack is therefore chiefly explained by their specific morphology.
The risk of caries in fissures is also increased significantly compared with smooth tooth surfaces if a fluoride prophylaxis is performed, since a fluoride prophylaxis cannot display the accustomed efficacy in the fissures.
By sealing the fissures, the relief of the tooth is flatter, the tooth is easier to clean and the development of caries can be prevented in this way. Sealing of fissures is nowadays acknowledged as a proven and recommended, effective prophylactic measure and is used ever more widely in daily dental practice. The rule is that all fissures and pits at risk from caries should already be sealed as a precaution. It has been possible to demonstrate that such a procedure leads to a significant decrease in cariogenic microorganisms in the fissure underneath the seal.